Say whether the sump is skimmed. An emulsifier designed to reject tramp oil fails its job if the oil is stirred back in.
Reject or absorb
A rejecting emulsifier lets tramp oil float so a skimmer can remove it. The coolant concentration stays closer to the blend you diluted. An absorbing emulsifier keeps one phase and then slowly becomes a different fluid, richer in the leaked oil and poorer in the additives you paid for.
Esteem emulsifier and ester packages can be aimed at either design. The purchase order has to say which. A lab that stirs the beaker for five minutes will hide a rejecting system and then call it unstable.
What else looks like tramp oil
Hard-water soaps and aluminium soaps cream in a way that operators call tramp oil. A solvent wash of the cream tells you if it is mineral oil. If it is soap, the fix is hardness and alkali, not a skimmer.
Log concentration by refractometer and by acid split if you have it. Refractometers drift when tramp oil dissolves into the reading.
| Design | Needs | Fails when |
|---|---|---|
| Reject tramp oil | Skimmer and quiet sump | Oil is continuously sheared back in |
| Absorb tramp oil | Biocide and dump schedule | You expected a clean float |
| Hard-water soap | Soft water or chelate | You skim a scum that is not oil |
| Foam after a leak | Identify the leaked additive | You add random defoamer |
Rejection is a designed failure of mixing
A soluble oil or semi-synthetic is built to emulsify its own base oil. Tramp oil is a different hydrocarbon, often with its own additives. If the emulsifier blend is rich and the droplet size is very small, the sump has unused emulsifier and the tramp oil disappears into the emulsion. The fluid then thickens, the pH drifts, and bacteria get a food source.
Rejection means the foreign oil stays as a separate layer. Skimmers and coalescers can remove it. That behaviour comes from a limited emulsifier reserve and from a hydrophilic–lipophilic balance that is enough for the concentrate oil and not enough for the hydraulic oil. It is not automatic.
What shear and hardness do
Pumps and nozzles shear tramp oil into droplets small enough to stay suspended even when the chemistry would rather split it. A quiet beaker split does not predict a high-pressure sump. Run the rejection test with shear if the machine has it.
Hardness and dissolved metals from the cut consume anionic emulsifiers. The emulsion can flip from “too stable” to “split” over a week without a formulation change. A weekly check of concentration, pH, and tramp layer thickness tells you which side of that flip you are on.
How to specify the split you want
Say whether the plant skims tramp oil or whether any split is a customer complaint. Those customers need opposite emulsifier reserves. Also name the tramp oil if you know it. Way lube and hydraulic oil do not stress a formula the same way.
Do not “fix” a tramp-oil complaint by adding more emulsifier unless the failure is cream in fresh water. Extra emulsifier is how a rejecting system becomes an absorbing one. Confirm concentration first. A weak dilution splits for a simpler reason: there is not enough emulsifier left for the original oil.
How to Specify with Esteem
- Identify the tramp oil: hydraulic, way lube, or rust-preventive.
- Say if a skimmer or centrifuge is installed and used.
- Give hardness and daily top-up rate.
- Describe the failure: cream layer, coarse split, or sudden foam.
- Choose reject or absorb as the design intent and hold the trial to that intent.
Pair this with the semi-synthetic HLB note and metal chemicals.